Quite frequently, mineral concentrates or ores are tainted with significant amounts of arsenic and antimony. At the time of the smelting of such substrates, the presence of these contaminants can generate substantial penalties or even preclude their treatment.
In order to circumvent such difficulties, several hydrometallurgical processes have been developed to extract the arsenic and the antimony contaminants from the raw ore or concentrate prior to the collection of metallic values therefrom.
In U.S. Pat. No. 3,911,078, Nadkarni et al. report the dissolution of arsenic from a copper ore of the enargite type (Cu3AsS4) using a basic solution of Na2S as extractive medium. The arsenic is recovered as sodium thioarsenate and if antimony is present, it is transformed into sodium thioantimonate. These thioarsenate and thioantimonate can be crystallized out from the mother liquor for safe disposal of As and Sb. Nadkarni et al. teach the use of pressure oxidation of the thiosalts of arsenic and antimony in order to substitute oxygen to sulfur on As and Sb, this oxidation being followed by precipitation of As and Sb as hydrated ferric arsenate (scorodite) or as hydrated ferric antimonate.
Several other patents are related to As and Sb extraction, such as U.S. Pat. No. 3,709,680, U.S. Pat. No. 3,911,078 and US Patent Application US2014/0017152A1 for example. These methods use basic sodium sulfide Na2S, sodium hydrosulfide hydrate NaSH or sodium hydroxide NaOH as the extractive reagents. The disposal of the extracted arsenic varies from merely discarding sulfides in tailings to the forming calcium arsenate or a hydrated ferric arsenate such as scorodite. However, disposal of the sulfide as such is to be avoided, environmentally and economically, particularly if the upkeeping of the landfill in the long term is taken into account. As far as calcium arsenate is concerned, this inorganic compound is vulnerable to potential leaching, particularly in sulfur-containing media, under a bacterial action (thiobacillum ferrooxidan). Finally, scorodite is reported to be unstable in the presence of significant sulfate concentrations, unless a high ratio of iron to arsenic, i.e. Fe/As between 2 and 4, is used to achieve the precipitation. This renders the formation of scorodite rather expensive, along with a need for elaborate burial procedures.
Therefore, it appears that improvement at the level of disposal of arsenic and antimony extracted from arsenic-containing ores or concentrates such as enargite and arsenopyrite for example are desirable from the present state of the art.
The present description refers to a number of documents, the content of which is herein incorporated by reference in their entirety.